PROJECT SUMMARY Systemic lupus erythematosus (SLE) is an autoimmune disease that progresses to self-tissue destruction and subsequent organ failure. These manifestations are caused by autoantibody secretion, immune complex deposition, and subsequent inflammatory responses. TLR7 and TLR9 play key roles in the loss of peripheral B cell tolerance. TLR signaling in B cells promotes their activation, autoantibody production, and resultant kidney pathology. Targeting factors downstream of TLRs provides a promising therapeutic option as TLR signaling critically regulates B cell responses in autoimmunity, but is generally not required for B cell responses to foreign antigen. While TLR signaling studies have focused almost exclusively on transcription factors, miRNAs also provide a substantial level of intracellular genetic and phenotypic control. Concurrently, several miRNAs have been shown to crucially contribute to SLE development. However, the interplay between TLRs and induction of miRNAs in SLE, and delineation of their critical mRNA targets have to date not been explored. Our goal is to identify autoimmunity-associated miRNAs induced by TLRs and their targets in B cells. Our preliminary data are the first to demonstrate that miR-21 is induced by TLRs in B cells. Since miRNA dysregulation contributes heavily to SLE disease development, this finding introduces an additional element of genetic control downstream of a critical receptor. Importantly, the delineation of miRNA-mediated disease mechanisms provides important therapeutic implications. miRNA-centric therapeutics have the potential for more precise targeting of dysregulated pathways compared to currently available therapeutic options. Given the dampening of SLE manifestations upon miR-21 anatagonism in a mouse model of SLE, in this proposal, we aim to determine the role and targets of miR-21 in TLR7-driven autoimmune B cell responses and SLE-like autoimmunity (Aim-1). Identifying the targets of miR-21 will help explore mechanisms and the signaling pathways by which miR-21 contributes to autoimmune B cell responses and autoimmunity. Because TLR7 and TLR9 play key roles in autoimmune B cell responses and autoimmunity in both mice and humans, we also aim to identify other autoimmunity-associated miRNAs induced by TLR7 and TLR9 in B cells (Aim-2). Identification of these miRNAs will provide critical data needed to pursue future in vivo signaling studies.